But here's another perspective on the price: Dropbox was valued at $4 billion in its last private financing. It is probably worth more today—say $5 billion, based on Dropbox backer Paul Graham's rough estimate.

So $100 million is just 2 percent of Dropbox's total value. That doesn't seem like a huge price to pay to launch Dropbox into a new market and add 13 employees (including, by the way, Adam Cue, son of top Apple executive Eddy Cue).